1. Field of the Invention
The present invention relates to an exposure apparatus and an exposure control method and more particularly to a slit scan type exposure apparatus equipped with an exposure control device for controlling an exposure amount and uniformity of luminous intensity to a sensitive substrate within a predetermined range wherein a mask and the sensitive substrate are scanned synchronously to expose a pattern of the mask on the photosensitive substrate an exposure method by use with the apparatus.
Also, the present invention relates to an exposure control device for controlling an exposure amount and uniformity of luminous intensity to a sensitive substrate within a predetermined range and an exposure control method for the same.
2. Related Background Art
In manufacturing semiconductors, liquid crystal display devices or thin film magnetic heads, etc. under photolithography technique, projection exposure apparatuses have been utilized in which the pattern of a photomask or a reticle (hereinafter called the reticle) is exposed via a projection optical system on a photosensitive substrate such as a wafer with photoresist applied thereto, a glass plate or the like. Recently, a chip pattern of a semiconductor, etc. tends to become large and in the projection exposure apparatus, it is required to expose a larger portion of the pattern of a reticle on the photosensitive substrate.
Also, as the pattern of a semiconductor, etc. becomes minute, improvement of resolution of the projection optical system is required. In order to improve the resolution of the projection optical system, the exposure field of the projection optical system needs to be enlarged, which but is difficult in respect to the design or manufacture. Especially, when using a reflective and refractive system as the projection optical system, there is a case that the shape of the exposure field with no aberration happens to be circular.
In order to deal with the problems of the tendency of enlargement of the pattern to be exposed and the limitation of the exposure field of the projection optical system, a method has been proposed in which a reticle and a photosensitive substrate are scanned synchronously with respect to, e.g., a rectangular, circular or hexagonal illumination area (hereinafter called the slit-shaped illumination area). That is, a so-called slit scan type projection exposure apparatus has been developed in which the pattern of a reticle larger than a slit-shaped illumination area on the reticle is exposed on a photosensitive substrate, as disclosed in U.S. Pat. No. 4,822,975.
Generally, in the projection exposure apparatus, the condition of a proper exposure amount and uniformity of luminous intensity with respect to a photosensitive material of the photosensitive substrate is determined. Therefore, the slit scan type projection exposure apparatus is also provided with an exposure amount control device which makes an exposure amount to the photosensitive substrate coincide with a proper exposure amount within a predetermined allowable range and maintains the uniformity of the luminous intensity of exposure lights to the photosensitive substrate within a predetermined level.
Also, recently, it is required to enhance the resolution of the pattern to be exposed on the photosensitive substrate. A method for enhancing the resolution is to use shortwave exposure lights. Among presently usable light sources, an excimer laser light source, a pulse oscillation type laser source (pulsed light source) such as a metallic vaporization laser light source or the like emits shortwave exposure lights. However, the exposure energies (light amounts) of pulsed lights emitted from the pulsed light source are fluctuated for the respective pulses within a predetermined range.
Consequently, the exposure amount control device is controlled such that after the end of exposure, an integrated exposure amount becomes a proper exposure amount within an allowable range. In the conventional exposure amount control device, when the average pulsed light amount of pulsed lights from the pulsed light source is  less than p greater than  and the range of the fluctuations of the light amounts of the pulsed lights is xcex94p, the parameter xcex94p/ less than p greater than  representing the fluctuations of the light amounts of the pulsed lights is deemed to become a normal distribution (actually random).
When the number N of pulsed lights emitted so as to be the proper exposure amount (to a certain area (pulsed light integrated area) on the photosensitive substrate which is scanned relatively with respect to an exposure area conjugate to the slit-shaped illumination area) is N, the exposure amount control device is controlled by using the fact that the fluctuations of the integrated exposure amount after the end of exposure becomes (xcex94p/ less than p greater than )/Nxc2xd.
When performing exposures by use with the pulsed light source in the slit scan exposure method, how the light emission timing of the pulsed light source is set becomes a problem. For this matter, conventionally, when scanning the reticle and the photosensitive substrate synchronously, a light emission trigger signal is sent to the pulsed light source each time a stage on the side of the substrate is moved for a predetermined distance. That is, a length measurement unit (e.g., laser interferometer) which measures the moving amount of the stage on the side of the substrate for scanning the substrate is utilized. And, light emission is performed in synchronism with the output of the length measurement unit.
In the above conventional technique, although the fluctuations of the light amounts of the pulsed lights emitted from the pulsed light source is taken into consideration, the fluctuations of the light emission timing (the fluctuations of periods when the pulsed light source actually emits a pulsed light each time after a light emission trigger signal is sent to the pulsed light source) are not taken into consideration. However the inventors of the present invention found that the light emission timing of the pulsed light source affects the control accuracy of the exposure amount and the uniformity of luminous intensity.
Further, generally, in the length measurement unit (laser interferometer or the like), there are fluctuations of the time when after performing actual measurement, it outputs the result of the measurement. Therefore, in such a method for making the pulsed light source emit a pulsed light in synchronism with the output of the length measurement unit, the fluctuations of the timing of reading the measurement result is added to the light emission timing of the pulsed light source. Accordingly, it is not possible to maintain the control accuracy of the exposure amount and the uniformity of luminous intensity within the allowable range because of the influence of the fluctuations of the timing reading the measurement results and the light emission timing of the pulsed light source.
In view of the above problems, it is an object of a present invention to provide an exposure apparatus capable of improving the control accuracy of an exposure amount and the uniformity of luminous intensity to a photosensitive substrate when exposing a pattern of a mask on the photosensitive substrate by use with a pulsed light source in a slit scan exposure method.
For achieving the above and other objects, an exposure apparatus for transferring a pattern on a mask to a substrate comprises a light source for emitting pulsed lights; an illumination optical system for illuminating the mask with the pulsed lights; a mask stage supporting the mask and being movable in a predetermined plane; a substrate stage supporting the substrate and being movable in a plane parallel to the predetermined plane; a drive section for moving the mask stage and the substrate stage synchronously; input means for inputting fluctuations of energies of a plurality of pulsed lights and fluctuations of the light emission timing of the plurality of pulsed lights; first calculating means for calculating the minimum number of pulses for a predetermined number of pulsed lights to be emitted to the substrate based on the fluctuations of the energies of the plurality of pulsed lights and the fluctuations of the light emission timing of the plurality of pulsed lights; second calculating means for calculating the moving speed of the mask stage and the substrate stage based on the light emission timing of the plurality of pulsed lights and the minimum number of pulses; a drive control section for controlling the drive section so as to move the mask stage and the substrate stage synchronously based on the calculated moving speed; and a control section for outputting a signal to said light source at regular intervals to emit said pulsed lights.
According to the above embodiment, not only the fluctuations of the energies of the pulsed lights but also the fluctuations of the light emission timing are taken into consideration, the control accuracy of the exposure amount and the uniformity of the luminous intensity is improved. Also, the light emission triggers are supplied to the pulsed light source at regular intervals and the scan speed of the mask is the same with that of the photosensitive substrate, so that the control accuracy of the exposure amount and the uniformity of the luminous intensity is further improved without being influenced by fluctuations of the timing of reading the measurement result of a length measurement unit such as a laser interferometer.
It is an object of the present invention to provide an exposure method capable of improving control accuracy of an exposure amount and uniformity of luminous intensity to a photosensitive substrate when exposing a pattern of a mask on the photosensitive substrate by a pulsed light source in a slit scan exposure method.
For achieving the above and objects, in a second preferred embodiment, in a method of transferring a pattern on a mask to a substrate by use with a light source for emitting pulsed lights, an illumination optical system for illuminating the mask with the pulsed lights, a mask stage supporting the mask and being movable in a predetermined plane, a substrate stage supporting the mask and being movable in a plane parallel to the predetermined plane and a driven section for moving the mask stage and the substrate synchronously, there are the step of inputting fluctuations of respective energies of a plurality of pulsed lights and fluctuations of light emission timing of the plurality of pulsed lights prior to exposing the substrate; the step of calculating the minimum number of pulses for a predetermined number of pulsed lights to be emitted to the substrate based on the fluctuations of the energies of the plurality of pulsed lights and the fluctuations of the light emission timing of the plurality of pulsed lights; the step of calculating a moving speed of the mask stage and the substrate stage based on the light emission timing and the minimum number of pulses; the step of moving the mask stage and the substrate based on the calculated moving speed; and the step of emitting the predetermined number of pulsed lights at regular intervals at the time of exposing the substrate.
Also, it is an object of the present invention to provide an exposure control device capable of improving the control accuracy of an exposure amount and the uniformity of the luminous intensity to a photosensitive substrate.
For achieving the above and other objects, in a third preferred embodiment, in an exposure control device being provided in an exposure apparatus which has a pulsed light source for emitting pulsed lights in accordance with respective light emission trigger signals from outside the pulsed light source, an illumination optical system for illuminating a predetermined illumination area on a mask with the pulsed lights and scan means for scanning the mask and a substrate relatively with respect to the predetermined illumination area and exposes a pattern of the mask on the substrate while scanning the mask and the substrate relatively with respect to the predetermined illumination area, the exposure control device being for controlling an integrated exposure amount of the pulsed lights to the substrate and uniformity of luminous intensity on the substrate within predetermined accuracy, there is monitor means for measuring an energy of each of the pulsed lights to be emitted to the substrate and light emission timing of the pulsed lights; a control section for emitting a plurality of pulsed lights from the pulsed light source prior to exposing the substrate; first calculating means for calculating the average value of the energies of the plurality of pulsed lights and fluctuations of the light emission based on the measurement result of the monitor means; second calculating means for calculating the minimum number of pulses for a predetermined number of pulsed lights to be emitted to the substrate based on the fluctuations of the pulse energies and the fluctuations of the light emission timing calculated by the first calculating means, the minimum number being necessary for controlling the integrated exposure amount to the substrate and the uniformity of luminous intensity on the substrate within the predetermined accuracy; light amount control means for controlling the energies of the predetermined number of pulsed light to be emitted to the substrate based on the minimum number of pulses for the predetermined number of pulsed lights, a proper exposure amount and the average value of the plurality of pulse energies obtained by the first calculating means; and light emission control means for supplying the light emission trigger signals at regular intervals to the pulsed light source so as to emit the respective pulsed lights.
Also, it is an object of the present invention to provide an exposure control method capable of improving the control accuracy of an exposing amount and the uniformity of the luminous intensity to a photosensitive substrate.
For achieving the above and other objects, in a fourth preferred embodiment, in an exposure control method for controlling an integrated exposure amount of a predetermined number of pulsed lights emitted from a pulsed light source to a substrate and uniformity of luminous intensity on the substrate in predetermined accuracy, there are the first process of obtaining, by emitting a plurality of pulsed lights from the pulsed light source prior to exposing the substrate, the average value of respective energies of the plurality of pulsed lights, fluctuations of the energies of the plurality of pulsed lights and fluctuations of light emission timing of the plurality of pulsed lights;
the second process of obtaining the minimum number of pulses for the predetermined number of pulsed lights to be emitted to the substrate based on the fluctuations of the energies and the fluctuations of the light emission timing obtained in the first process, the minimum number being necessary for controlling said integrated exposure amount to the substrate and the uniformity of luminous intensity on the substrate within the predetermined accuracy;
the third process of controlling the energies of the predetermined number of pulsed lights to be emitted to the substrate based on the minimum number of pulses, a proper exposure amount to the substrate and the average value of the energies obtained in the first process; and
a fourth process of sending a light emission trigger signal at regular intervals to the pulsed light source so as to emit the pulsed lights.